1. Field of the Invention
The present invention relates generally to fixed cutter bits of the type used in cutting geological formations such as used in drilling a borehole for completing an oil well or the like. More particularly, the invention relates to fixed cutter bits for attachment to a well casing for effecting simultaneous drilling and casing of a borehole.
2. Description of the Prior Art
In drilling a borehole through a formation it is normal procedure to connect a drill bit on the lower end of an assembly of drill pipe sections which are connected end-to-end so as to form a drill string. An apparatus that is positioned above the surface of the borehole rotates the drill string. The apparatus turns the drill string and advances it downwardly, causing the bit to drill through the formation. During drilling, drilling fluid is pumped through the drill string and directed out of the bit through ports or channels formed in the bit. The drilling fluid is provided to cool the bit and to wash away cutting debris.
Once the drill string has reached a desired depth, the string is removed and a well casing is lowered into the borehole for completing the well. Depending on the required depth of the borehole, this process may need to be repeated several times to reach the desired depth. This process is normally very expensive and time consuming due to the time it takes to drill the borehole, remove the drill string and run-in the well casing. In addition, while removing the drill string and running in the well casing a cave-in can occur obstructing the well casing from advancing downward through the borehole.
With the above mentioned drawbacks, it is desirable to minimize the work and expense required to complete a well by utilizing the well casing or well liner as the drill string which is left in the borehole upon completion of drilling, thereby not requiring the use of a separate casing or liner to be run-in upon removal of the drill string.
Therefore, a need exists for a new and improved bit that can be used for drilling while casing. In this regard, the present invention substantially fulfills this need. In this respect, the bit according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of drilling while casing.